There was a recent thread on another board about this subject. I hope it's OK to quote Ralph Cutter from that thread. He said "... in fact have witnessed many hundreds of caddisfly pharate adults generate air underneath their cuticle in both rivers and lakes." Ralph's and Gary's observations are good enough for me to believe that Caddis pupa do generate a gas bubble that can be imitated by the Sparkle pupa patterns and other patterns. That's not to say that these patterns can't also imitate a diving caddis.